Sahara
The world's largest hot desert, an ocean of sand and stone across North Africa
The Sahara is less a place than a continent within a continent, a sweep of sun-scorched rock and dune that swallows nearly a third of Africa. Spanning some 9.2 million square kilometres, it stretches from the Atlantic surf of Mauritania to the Red Sea coast of Egypt, a distance comparable to the breadth of the United States. Its name, from the Arabic for desert, undersells the variety within: towering ergs of wind-sculpted sand, gravel plains, salt flats, and volcanic massifs whose peaks catch occasional snow.
Only about a fifth of the Sahara is sand sea. The rest is hamada, bare rock scoured by wind, and reg, expanses of pebbles polished to a desert pavement. The Tibesti and Ahaggar mountains thrust volcanic cones above 3,000 metres, while the Qattara Depression in Egypt sinks more than 130 metres below sea level. Daytime temperatures routinely exceed 45 degrees Celsius, yet nights can plunge toward freezing. Beneath the surface lie vast fossil aquifers, water trapped during wetter epochs when grasslands, rivers, and lakes covered the region only a few thousand years ago.
Human life has clung to the Sahara for millennia, recorded in the rock art of the Tassili n'Ajjer, where ancient painters depicted cattle, swimmers, and giraffes long since vanished. Camel caravans of the Tuareg and Berber peoples once carried gold, salt, and captives along trans-Saharan routes linking sub-Saharan kingdoms to the Mediterranean. Today the desert remains sparsely peopled, its oases and river valleys supporting agriculture, while its sands hold oil, gas, and ambitions for vast solar arrays that could one day power distant cities.